The present invention relates to a magnetic recording and reproducing apparatus having a variable speed reproducing function for reproducing a video signal which has been recorded with an H alignment which deviates between adjacent record tracks, and which is applicable, but not exclusively, to an 8 mm video tape recorder (VTR), etc.
In general, in a helical scan type VTR which carries out recording and reproduction of a video signal by means of at least one rotary magnetic head, the video signal corresponding to one field is sequentially recorded through a predetermined azimuth angle of the head on each slanted recording track on a magnetic tape. A four-head type VTR has conventionally been used in which a pair of normal playback heads are alternated with a pair of auxiliary heads each having an inverse azimuth angle with respect to each normal playback head and used for a variable speed reproduction so that the variable speed reproduction operation can carried out.
When the variable speed reproduction is carried out by such kinds of VTRs, the continuity of the horizontal synchronization (H) can be maintained even in a track jump operation provided that recorded positions of horizontal synchronization signals of the video signal on the magnetic tape are aligned between adjacent tracks, i.e. a record format which has taken an H alignment. It is noted that the H alignment is represented by a distance between respective record starting points of adjoining tracks divided by a length of one horizontal synchronization period. If the value of H alignment=0.5H.times.(odd number), since one field=262.5H, the tracks are completely aligned.
On the other hand, in a record format which deviates from H alignment between adjoining tracks, it is necessary to delay the reproduced video signal from the recorded tracks by a constant interval of time in order to correct for the deviation of the H alignment.
For example, an 8 mm VTR has an LP (Long Play) mode of the record format which takes an H alignment (0.5H alignment) as shown in FIG. 5 and an SP (Standard Play) mode of the record format in which the H alignment is deviated (1.0H alignment) as shown in FIG. 6.
FIG. 7 shows a conventional head arrangement of a four-head type 8 mm VTR in a rotary drum.
As shown in FIG. 7, suppose that a gap interval (GL) between each normal playback head A, B and each auxiliary head A', B' used for the variable speed reproduction corresponds to 2H. It is, then, necessary to delay the reproduced video signal by 0.5H to correct for the deviation of H alignment when the reproduced video signal is derived through the auxiliary heads A', B' in the SP track pattern mode. Therefore, in the conventional method, an 8 mm VTR having a variable speed reproduction operation mode is provided with a 0.5H delay line 63 having a delay corresponding to 0.5H in the processing system for the reproduced luminance signal PB.Y, as shown in FIG. 8, so that continuity of H is assured.
FIG. 8 is a block diagram of a conventional VTR. A reproduced video signal PBmain derived through the normal playback head 52 from the magnetic tape 51 and another reproduced video signal PBsub derived through the auxiliary head 53 are amplified through respective playback amplifiers 54, 55 and sent to a Y/C separation circuit 57 via a signal selection switch 56.
FIG. 9 shows a timing chart indicating the operation of a conventional 8 mm VTR. It is noted that in the SP mode, the reproduced video signal PBmain derived through the normal playback head 52 is reproduced 0.5H in advance of the reproduced video signal PBsub obtained through the auxiliary head 53, as shown in FIG. 9.
In addition, the selection switch 56 is responsive to a head select signal HS to select either of the two reproduced video signals. The timing of the head select signal HS is such that one of the reproduced video signals PBmain, PBsub is selected which has been derived during the tracing of the normal playback head 52 and the auxiliary playback head 53 on their corresponding azimuth angle recorded tracks when variable speed reproduction is carried out.
The Y/C separation circuit 77 separates the reproduced video signal received via the signal section switch 56 into a luminance signal Y and a chromatic signal C. The luminance signal Y is sent to a demodulation circuit 58. The chromatic signal C is sent to a signal mixer 60 via a chromatic signal processing circuit 59. The reproduced luminance signal PB.Y derived by the demodulation circuit 58 is sent to a 1H delay line (1H DL) 62 or to a 0.5H delay line (0.5H DL) 63 via signal selection switch 61 for drop out compensation. Furthermore, the luminance signal PB.Y is sent to a synchronization separation circuit 65.
The signal selection switch 64 is responsive to the head select signal HS together with the signal selection switch 56 in the variable reproduction operation mode. The reproduced luminance signal PB.Y is sent to the synchronization separation circuit 65 and to the signal mixer 60 via the 0.5H delay line 63 during a selected interval Tsub of the auxiliary head 53. It is noted that the signal selection switch 61 and 1H delay line 62 constitute a drop out compensation circuit in a normal speed reproduction operation mode. When the drop out occurs, the reproduced luminance signal PB.Y with a 1H delay is sent to the synchronization separation circuit 65 and to the signal mixer 60. The signal mixer 60 synthesizes the reproduced video signal PBout from the reproduced chromatic signal and luminance signal and outputs the reproduced video signal PBout via a signal output terminal 66.
In the conventional 8 mm VTR in which the continuity of H is assured in the variable speed reproduction mode with the 0.5H delay line provided in the processing system of the reproduced luminance signal PB.Y, only the luminance signal Y can be corrected. In addition, an out-of-synchronization part (Da), an image deviation part (Db), and black color drop part (Dc) occur in the reproduced video signal PBout as shown in the timing chart of FIG. 9 so that the variable speed reproduction operation cannot be carried out with good picture quality.